Patient-specific dosimetry in CT

Abstract

Radiation originated from CT examinations has been identified as the major contributor of radiation dose to patient population from medical purposes in the United States. Therefore, there is a great concern regarding the risk associated with radiation exposure from these examinations in both children and adults. Although effective dose has been the most commonly used dose metric when reporting the risk related to a given type of procedure, it has been recently suggested that the radiation dose delivered to specific radiosensitive organs should be determined. Physical anthropomorphic phantoms and mathematical models have been widely used for this purpose. However, the variability of human anatomy may be significant, especially for pediatric patients. In addition, modern CT scanners are equipped with automatic tube current modulation systems (TCM), which allow for images at reduced patient radiation dose. These systems modulate the tube current depending on the patient body size. Consequently, the dose reduction due to the activation of the TCM will considerably vary for patients with different body habitus. Methods based on voxelized patient models have been developed to individualize patient radiation dose. Size-specific, scanner-independent ‘CTDIvol to organ’ dose conversion factors have been produced to estimate organ doses from various CT examinations. Patient’s sex, body status and TCM settings should be taken into account in patient specific CT-dosimetry. In this presentation methods developed to determine individual-specific organ doses from CT examinations, based on patient specific models, will be reviewed.